Sampling of a continuous signal is performed by a sampler (sampling circuit) that takes out a signal value of a continuous signal for each of a plurality of sample points which have a fixed interval. When the continuous signal is an analog signal, a discrete signal (sampling signal) turns into a digital signal by being quantized and coded. A digital signal thus subjected to analog-digital conversion is reproduced as a continuous signal via a discrete signal in an digital-analog conversion. For sampling performed with a fixed interval, a method of obtaining a reproduction signal from a discrete signal by convoluting operations on a discrete signal and a sampling function is known (e.g., Japanese Patent Laid-open No. 2000-13226).